The heat in the IRS investigation just went up. Rep. Darrell Issa, head of the House Committee on Oversight and Government Reform, sent a letter today to ranking member Rep. Elijah Cummings in which he accuses Cummings of working to “obstruct the investigation” into IRS misbehavior.

The bulk of Rep. Issa’s letter is devoted to some recently uncovered emails which demonstrate that Rep. Cummings was seeking information on True the Vote, the voter integrity group based in Texas which became the target of much unwanted government attention.

Cummings’ staff contacted the IRS in August 2012 to inform them that they would be opening an investigation into True the Vote’s activities. Then in October 2012 Cummings’ office began requesting information directly from True the Vote which was very similar to what had previously been requested by the IRS.

For instance, in February the IRS requested information True the Vote’s software and training materials. Rep. Cummings office also asked for information on True the Vote’s software and training materials in their October 2012 request. Issa’s letter suggests the similarities might be more than a mere coincidence, “This timeline and pattern of inquiries raises concerns that the IRS improperly shared protected taxpayer information with your staff.”

Five days after Rep. Cumming’s first letter to True the Vote in October 2012, in which he requested information on “training materials used for volunteers,” the IRS sent True the Vote another request asking for information on volunteers and training.

Then in January 2013, Cummings’ office sent a request for information on True the Vote public tax information to the IRS. This request was handled by Holly Paz with oversight from Lois Lerner. Eventually Paz did forward copies of public information back to Rep. Cummings staff. However this transaction was, according to Issa’s letter, never mentioned to the Majority staff even after Paz and Lerner became a focus of the IRS targeting investigation.

Issa’s letter closes with a demand that Rep. Cummings “explain the full extent of you and your staff’s communications with the IRS and why you chose to keep communications with the IRS from Majority Members and staff even after it became a subject of controversy.”

Rep. Issa and Rep. Cummings have been at odds over the IRS matter for months. The tension seemed to reach a new high last month when Issa cut Cummings’ microphone as Rep. Cummings was launching into a loud speech clearly intended to highlight his outrage. Issa later apologized for his behavior but that didn’t stop Democrats from suggesting Issa should lose his Chairmanship over the incident.